Allying with the Mon Calamari Rangers, Sinde assisted them by advising them on military tactics and strategies, and helping them defend the Mon Calamari refugees who had taken refuge on the planet's ocean floor. After several months, Sinde was able to contact Emperor Fel on Bastion, and was ordered to return as soon as possible to train new Imperial Knights. Despite feeling that his work on Dac was crucial, he was prepared to obey his Liege's orders. However, at the same time, the Sith scientistVul Isen created a Sea Leviathan to hunt down the Mon Calamari refugees and suck them dry of their life-energies. When word of its existence reached Sinde, he initially counseled the Rangers to leave it alone and sacrifice the refugees to safeguard the few Ranger units operating on the planet. When CaptainTanquar, leader of the Rangers, made it clear that would not happen, Sinde devised a plan to destroy the Leviathan. While the Rangers attacked Isen's AT-AT Swimmer that was riding herd on the creature, Sinde took command of a number of Devilsquids, six tentacled creatures that hunted Mon Calamari. Sinde directed them to attack the Leviathan, and they dragged it into the depths of the Devil's Crevasse, where the Devilsquids made their home. Returning to Ranger Grotto, Sinde reported to Fel that obtaining transport off the planet was impossible. Fel told the Knight to return when the situation was merely difficult, not impossible, and sent Sinde's former apprentice, Sigel Dare to retrieve him and return him to Bastion.

Sinde returned to Bastion following a confrontation with Master Dare, and the offer from Jedi MasterAsaak Dan—who had accompanied Dare to Dac—to take his place in guiding and assisting the Mon Calamari Rangers. Although he took up his post training new Imperial Knights, he accompanied Emperor Fel to the planet Agamar, where representatives from the Empire and Jedi Order were meeting to formalize an alliance to oppose the Sith Empire. During the trip to Agamar, Fel admitted to Sinde that training new Knights was not the only reason for ordering Sinde back to Bastion; the Emperor was fearful of corruption, and needed Sinde by his side to counsel him. On Agamar, Sinde, along with his fellow Knights, guarded Fel during the meeting with the Jedi delegation. As the meeting came to a close, MoffNyna Calixte, head of Imperial Intelligence in Darth Krayt's Galactic Empire, arrived to warn the congregation that the Sith knew of the meeting, and had arrived with the intention of capturing or killing the Emperor. During the subsequent battle with members of the One Sith, Sinde helped Antares Draco, leader of the Imperial Knights, evacuate the Emperor from the battle. Sinde later commanded the Imperial forces sent to defend the Jedi's Hidden Temple on Taivas from Sith-Imperial forces, and was aboard the flagshipJagged Fel during the Battle of Coruscant.

"We were unaware of Stazi's plan to "liberate" the vessel. The device is set to go off when the ship's weapons come online -- when we believed the ship would be far enough from Dac that the Mon Cals wouldn't be blamed."

With the Imperious-class Star DestroyerImperious nearing completion at the shipyards at Dac,[8] Emperor Fel authorized a mission to sabotage the vessel, denying its usage to Darth Krayt's Sith Empire. Sinde and Master Sigel Dare were dispatched to Dac to destroy the vessel. Infiltrating the Imperious, they planted three sets of explosives—they fully expected the first two sets to be found, but were confident the third set would remain undiscovered. They primed the explosives to go off when the ship's weapon systems came online during the vessel's shakedown cruise, reasoning that the ship would be far away enough from Dac at the time so that the Mon Calamari would not be blamed for the sabotage.[1]

However, AdmiralGar Stazi of the Galactic Allianceexecuted a bold mission to steal the Imperious for his own forces. Stazi succeeded in his plan, spiriting away the ship from Dac, although it cost him his own flagship, the Indomitable, in the process.[9] Sinde, realizing that the explosives would not be discovered by the Alliance, decided that they had to warn Stazi of the sabotage. Although Dare did not see the point—believing that the Alliance admiral was as much their enemy as the Sith—Sinde knew that Fel hoped to ally with Stazi and that, by warning the admiral, they might be able to convince him of their good intentions and convince him to enter into negotiations for an alliance with Emperor Fel.[1]

Sinde and Dare help to liberate Galactic Alliance pilots held prisoner on Dac.

To achieve their goal of warning Stazi, they needed to contact a member of the Alliance and get their assistance in relaying word to the Duros admiral. Tracking down Monia Gahan—niece of former Senator and Galactic Alliance Triumvirate member Gial Gahan—Sinde and Dare saved her from execution at the hands of a squad of stormtroopers and informed her of the situation. Gahan was a member of Rogue Squadron,[1] and had been assigned to slice into the Dac planetary defenses during Stazi's assault, co-opting them for use by the Alliance.[9] She agreed to help the Imperial Knights reach Stazi, but only if they assisted in the rescue of Alliance pilots captured during the battle. While Dare disagreed with risking themselves unnecessarily, Gahan convinced Sinde to participate in the rescue, pointing out that the successful liberation of the pilots would go a long way to convince Stazi of their sincerity.[1]

When the Knights and Gahan rescued the pilots—which included Rogue Squadron pilot Ronto—Sinde quickly laid out a plan to get them all off-planet. He instructed three of the pilots to put on stormtrooper armor, and with Dare posing as an Imperial lieutenant, the group moved up to the hangar levels where Dare used a mind trick to convince the captain on-duty that they were authorized to load the prisoners aboard the personal shuttle of Darth Azard, a Quarren Sith Lord. Sinde assisted in incapacitating the crew as the Alliance personnel boarded and prepped the ship for flight. Unfortunately for them, Azard had sensed a disturbance in the Force, and had tracked it to his shuttle. Sinde, waiting at the aft boarding ramp, saw Azard coming towards the shuttle with his lightsaber lit. He informed Dare of the situation, ordering her to get the shuttle off the ground and meet up with Stazi, then leapt from the back of the shuttle to engage Azard.[1]

Sinde and Azard dueled on the hangar level, and the Imperial Knight sought to stop the Sith Lord from raising the alarm. During the duel, Dare used the Force to maneuver a fuel tank attached to the shuttle into the path of its rear guns. Dare then commanded one of the Alliance pilots to fire on the fuel tank, causing a massive explosion on the hangar level that covered their escape. Sinde used the explosion to cover his own retreat from the duel with Azard, diving off the edge of the hangar level. Sinde survived the fall, joining up with one of the many resistance groups forming in the wake of Darth Krayt's massacre of the Mon Calamari Council, the first stage of a genocide ordered to punish their supposed participation in the theft of the Imperious. His willingness to sacrifice himself allowed Dare, Gahan and the Alliance prisoners to join up with the Alliance fleet, warning him of the explosives planted on the Advanced Star Destroyer, and broaching the subject of an alliance between Stazi's forces and Fel's.[1]

Sinde allied himself with the Mon Calamari Rangers, operating out of a hidden base known as Ranger Grotto. The Imperial Knight advised the Rangers in battle tactics and assisted them in defending the Mon Calamari refugees hiding in hidden camps on the ocean floor. However, Sinde knew that the Rangers did not have resources to remove the Sith and Imperial presence from Dac—they were simply fighting for time until the rest of the galaxy got their act together and united to drive the invaders from the planet.[7] Cut off from the Empire-in-Exile, Emperor Fel wondered if Sinde had survived as they had heard nothing from him in months. Master Dare insisted that Sinde was still alive, however.[2]

"We all should be proud, Master Sinde! We drove away an Acklay Battle Fortress! An Acklay!""You didn't drive it away, Tanquar. I did. And the reason we were shadowing it in the first place was to capture it. It would have provided a mobile fortress you Rangers badly need!"

Sinde devised a plan to capture the Acklay Battle FortressSea Lion—an Imperial war machine that operated underwater—by shadowing it with Rangers operating Krakana fighters. Sinde believed that the Acklay would give the Rangers a mobile battle platform that they badly needed. However, when the Acklay that they were tracking came across a refugee camp and began attacking it with Shark fighters, the Rangers abandoned the plan and launched a premature attack to protect their people. Sinde, clad in an underwater battle suit and wielding his lightsaber, joined the battle just as the Sea Lion dispatched seatroopers from Alpha Squadron. Using an inkbomb to blind the squad, Sinde engaged the seatroopers in combat, swiftly dispatching them by using the Force and his lightsaber.[7]

Sinde used the Force to propel himself into the Acklay's fight/flight deck, and began engaging Imperial forces within the battle fortress itself. During the fighting, blaster bolts hit one of the Acklay's fuel tanks, triggering an explosion on the deck that cracked the hull and allowed water to begin seeping in. Sinde was caught in the explosion and thrown across the deck; as he recovered, he came face to face with Chief Alsek, the Sluissi he had served with on the Intrepid years before. Alsek had a blaster rifle trained on the Imperial Knight, and demanded to know why he had attacked fellow Imperials. Sinde told him he served the rightful Emperor, while Alsek countered that he served the throne, not a single man. He followed the orders of his lawful superiors, and it was his duty to follow orders. Sinde replied that he had his own duty, and asked Alsek not to make him kill the Sluissi. Alsek, already mortally wounded by the explosion on the fight/flight deck, fired. Sinde deflected the bolt, sending it arcing back into Alsek, killing him.[7]

Sinde returned to the Ranger Grotto, and rebuked the leader of the Rangers, Captain Tanquar, when the Mon Calamari claimed they should be proud of their efforts in driving off an Acklay Battle Fortress. When Tanquar countered that they could not stand by while the fortress slaughtered their people, Sinde reminded the Mon Calamari that they needed to prioritize. He told them that they could not beat the Empire, and that their true goal was to hold on long enough for outside forces to come to their assistance. In a private conversation, Tanquar told Sinde that—despite their differing opinions—they were not ungrateful for his help. Sinde told the Mon Calamari about being forced to kill Alsek, a being who had served under him. Discussing loyalties and obedience to duty, Tanquar asked the Imperial Knight what would happen if Emperor Fel ordered Sinde to betray or abandon the Rangers. Sinde told him that he was glad to be where he was, able to help those in need. He held a deep respect for the Mon Calamari, and told Tanquar that he would never choose to betray him.[7]

To further the genocide on Dac, the Givin Sith scientist Vul Isen created a Sea Leviathan which could suck dry the life energy of any Mon Calamari it came into proximity of, instantly killing them. After testing it on the Mon Calamari incarcerated at Imperial Extermination Camp 28, Darth Azard—the Sith in charge of the extermination of the Mon Calamari population—ordered it to proceed to the location of the refugee camp that the Sea Lion had attacked in the hopes of drawing out the Rangers.[7] Isen and Azard accompanied the Leviathan in an AT-AT Swimmer to an area near the Devil's Crevasse. There, it encountered a pair of Krakana fighters piloted by the Rangers Shonmai and Adriphar. The two Mon Calamari managed to gather intelligence data on the beast, but Adriphar's fighter was shot down by the Swimmer. While attempting to escape, the Leviathan sucked Adriphar's life energy straight out of the Mon Calamari, killing the Ranger. Shonmai managed to escape, and headed back to Ranger's Grotto.[2]

Sinde and Tanquar in the Ranger's Grotto

In return for Sinde's assistance, the Rangers managed to build a communications unit that allowed him to contact Emperor Fel on Bastion. Fel ordered Sinde to return as soon as possible, as he needed the veteran to train more Imperial Knights. Sinde told him that he was doing essential work on Dac, and that his actions might lead to an alliance between the Empire-in-Exile and the Mon Calamari. Fel told him that the Mon Calamari had traditionally supported the Rebellion or the New Republic, and that they would never ally with the Empire. He expected the Knight to return at his earliest opportunity.[2]

The conversation had been overheard by Captain Tanquar, and a brief argument between the Mon Calamari and Sinde ensued. Tanquar appealed to Sinde, believing that his service to the Force meant that he should remain on Dac where he could make a difference. Sinde countered this, stating that Imperial Knights believed that they served the Force by serving an Empire that stood for order and stability. They were interrupted by the news that Shonmai had returned from patrol alone, and the pair went to hear his report. Shonmai relayed her encounter with the Leviathan, and that it was heading towards a refugee camp. Tanquar immediately ordered the Rangers to their Krakanas so that they could engage the beast.[2]

However, Sinde recognized that the creature was a Leviathan, and that any attack by the Rangers on it was doomed to failure. He told the Rangers of the creature's origins—that it was a product of Sith science—and that it would folly to throw away their lives on an assault on the beast. Incensed, Tanquar demanded to know whether or not Sinde was saying that they should sacrifice the refugees; Sinde replied that was the case, when it was necessary for the greater good. He pointed out that the Mon Calamari had precious few Ranger units, and needed every single one of the them. The Ranger captain told the Knight that his way—the Imperial way—was not the way of the Mon Calamari. Seeing that the Rangers were committed to the assault, Sinde relented and devised a possible plan to destroy the Leviathan. Although the Krakana the Rangers used would do nothing to the Leviathan, he surmised that they might be able to turn the beast if they attacked the AT-AT Swimmer riding shotgun with it. At the same time, two or three Rangers would lead the refugees to the Devil's Crevasse. The Rangers initially balked at this idea, since the Crevasse was so named as it was inhabited by Devilsquids, vicious six tentacled creatures that preyed on Mon Calamari. Sinde intended to use the Devilsquids to attack the Leviathan, using the Force to take control of the creatures. Tanquar asked the Knight why he was now willing to help them, to which Sinde replied that it was because the Ranger captain was his friend.[2]

As Tanquar led the Rangers in an assault on the AT-AT Swimmer, which was carrying both Vul Isen and Darth Azard, Sinde donned his underwater armor and took control of a large number of Devilsquid. Directing them towards the Leviathan, the Devilsquids used their tentacles to attack the creature, pulling at its flesh and scales, and dragging it towards the Devil's Crevasse. Sinde attacked the creature himself with his lightsaber, although the Leviathan attempted to drain his life energy. However, as the Leviathan had been bred to kill Mon Calamari only, the energy tendril from the creature did little injury to Sinde, although it did damage his armor. As the Devilsquid dragged the Leviathan down into the depths of the Devil's Crevasse, Sinde—his armor malfunctioning—was rescued by Tanquar. The Rangers had successfully destroyed the AT-AT Swimmer when Shonmai had sacrificed herself to ram the vessel as its shields were lowered to launch Shark fighters.[2]

Back at the Ranger's Grotto, Sinde again contacted Emperor Fel to warn him that the Sith had resurrected the Leviathan, and that Bastion should be put on alert. Fel noted this, then inquired as to Sinde's return to Bastion. The Knight asked when a transport would be sent for him. Fel was unable to spare any to pick him up, and Sinde noted that acquiring a transport off the planet was impossible at the time. Fel, noting that his father had warned him of Sinde's stubborn streak, told him to return when it was simply difficult, and not impossible. Following his report, Sinde met with Tanquar. He noted that their accomplishment over the Leviathan was not really a victory, and that they had simply won the right to fight for one more day. Tanquar, relieved that Sinde was staying with them, noted that, even if they did not have an ally in the Empire, they at least had a friend in Sinde.[2]

Shortly after, Master Dare was ordered by Emperor Fel to travel to Dac and retrieve Sinde. Fel, operating on intelligence that Darth Krayt may have perished during an assault on the planet Had Abbadon, believed—if Krayt really was dead—that a strike against the One Sith was a very real possibility.[10] Dare, who was with Admiral Stazi's Galactic Alliance Remnant fleet, requested the use of an Imperial shuttle from the captured Imperious—which had since been renamed Alliance. Stazi agreed, on the condition that TogrutaJedi MasterAsaak Dan accompanied her.[3]

Aware of Dare's mission to retrieve him, Sinde and Tanquar traveled to the appointed rendezvous. Welcoming his former apprentice, he shocked Dare by telling her that he would not be returning with her. Sinde believed that the Force was telling him to remain with the Rangers and continue his work, and felt it was more important than returning to Bastion to train new Imperial Knights. Dare insisted that Sinde was to obey Emperor Fel's orders, and ignited her lightsaber; Sinde implored her not to start a fight, as he had been the one to train her in the ways of the lightsaber. However, Dare was adamant; Sinde would return with her, or he would die on Dac. Dismayed that Dare believed that an Imperial Knight's duty was a matter of personal loyalty to Emperor Fel, and feeling that many of the younger Knights were losing sight of what an Imperial Knight was meant to be, Sinde began to duel her.[3]

Sigel Dare, Asaak Dan and Treis Sinde engage in a three way duel.

As the pair fought, Master Dan ignited his own lightsaber and intervened. Drawing their attention to him, he told Sinde that he agreed with Master Dare; specifically, that if Sinde thought that younger Imperial Knights were losing focus and forgetting that an Imperial Knight's duty was to the Force as embodied by the Emperor rather that obeying the Emperor above the will of the Force, then it was his duty to return to Bastion to train them correctly. However, Master Dan also saw that the Ranger's needed help, and offered to stay on Dac, taking Sinde's place. Seeing the wisdom in Dan's offer, Sinde accepted. He bade farewell to Tanquar, and prepared to leave Dac with Dare.[3]

Sinde returned to Bastion with Dare, and took up the position of training Imperial Knights. Shortly after returning, he oversaw a practice duel between Masters Ganner Krieg and Azlyn Rae.[11] Master Rae had been severely injured during a battle with Sith forces on the planet Had Abbadon,[12] and her life was saved by the outlaw tech Bantha Rawk who designed a special armor to keep her body functioning.[10] The armor was then redesigned and improved by the Master armorerHogrum Chalk, a former Imperial Knight. Sinde admonished Krieg for going easy during the duel, telling him that Rae needed to test her armor fully, and that it was better to find out if the armor was worthless in a practice duel rather than in actual combat.[11]

As the Empire, the Galactic Alliance and the Jedi Order began to realize the need to work together to overthrow the Sith Empire, a meeting was arranged between the Empire and Jedi on the planet Agamar. Emperor Fel travelled to the meeting aboard the Dauntless, a Pellaeon-class Star Destroyer, and took Master Sinde along with him. During the trip, the two sparred with their lightsabers, and Sinde deduced from their conversation that training Imperial Knights was not the only reason that Fel had brought him back from Dac. Fel admitted that he was fearful of being corrupted, and that the last seven years since his forced exile from Coruscant had been hard on him. Sinde—who had heard of his Emperor's intent to take possession of and use the Muur Talisman,[5] a Sith artifact capable of creating Rakghouls[13]—questioned Fel over whether or not he really intended to use it. Fel wondered if using the dark side of the Force to free the galaxy was justifiable; Sinde told him that it was not, and that it was too high a price to pay since Fel would just become another Krayt. He also reminded him that it was the duty of the Imperial Knights—including Fel's own daughter, PrincessMarasiah—to kill the Emperor if he turned to the dark side, since they looked to him for direction, and that he embodied their connection to the Force. Fel admitted to Sinde that he would have made him leader of the Imperial Knights were he not always so contrary. Sinde told Fel to let Antares Draco keep that job—Sinde had his hands full riding herd on Fel himself.[5]

On Agamar, Master Sinde and Fel—along with their fellow Imperial Knights Antares Draco, Ganner Krieg, Sigel Dare and Marasiah Fel—made camp for the night, and waited for the morning to attend the appointed meeting. Sinde felt the presence of the Jedi delegation, and relayed the information to Draco. The leader of the Imperial Knights felt that by leaving Bastion, the Emperor had exposed himself and his daughter to unnecessary danger. Sinde and Draco discussed the security arrangements surrounding the meeting; Sinde assured Draco that that secrecy would ensure their safety while Draco was wary of an attack upon the assembly. The discussion turned to one regarding Draco's priorities if an attack were to occur. Sinde—aware of Draco's love for the princess—questioned if the leader of the Imperial Knights could make the hard choice if he had to chose between saving one or the other. Draco assured him that he knew his duty, and questioned whether the elder Knight knew his. Sinde stated that his place was at the Emperor's side.[14]

The following morning, Emperor Fel and the Imperial Knights met with the Jedi delegation, which was led by the Whiphid Jedi Master K'Kruhk, a member of the Jedi Council. During the meeting, the two parties agreed to a formal alliance, with Emperor Fel allowing Bastion to serve as a safe haven for both the Jedi and the Galactic Alliance. As the meeting drew to a close, Master Draco sensed an intruder approaching the meeting place, riding a local animal. As the beast and its rider drew closer, Master Sinde gave the order to open fire on it. Masters Krieg and Dare opened fire with their blasters, striking the beast, and causing the rider to implore them to stop firing. Emperor Fel recognized the voice as belonging to Nyna Calixte, a High Moff serving on Darth Krayt's Council of Moffs and head of Imperial Intelligence. Despite the fact that she was an enemy, Fel ordered his Knights to cease fire. Calixte, held at lightsaber point, hurriedly told the assembled Imperial Knights and Jedi that the Sith were aware of their meeting, and had sent a task force under the command of MoffRulf Yage to capture or kill the Emperor. As the task force, led by the Pellaeon-class Star Destroyer War Hammer, engaged Fel's Dauntless in orbit, Calixte informed the assemblage that they had to run if they were to survive.[14]

Treis Sinde engages the Sith in combat

Calixte's warning was too late, however; members of the One Sith emerged from underwater, igniting their lightsabers and preparing to engage the assembled Jedi and Imperial Knights. Master Draco gave the order for the Imperial Knights to defend the Emperor and Sinde stood ready with his fellow Knights; in addition to the Knights assembled around the Emperor, several more members of the organization revealed themselves to the One Sith, having been disguised as Agamarian farmers. Master K'Kruhk also ordered his Jedi to defend the Emperor, and battle with the One Sith was joined. As the battle raged, Master Draco called for their shuttle, Defender One, to move to their position to evacuate the Emperor immediately. As the shuttle moved in, Sinde and Master K'Kruhk began clearing a path to the vessel, which landed and began evacuating the assembled combatants. Although the Emperor was aboard, three individuals remained outside—Marasiah Fel, Azlyn Rae, and the Jedi Master Rasi Tuum. One Sith starfighters were closing on their position, and Sinde reminded Draco that the Emperor had to survive at all costs and that he should give the order to evacuate despite his personal feelings. Watching as the enemy starfighters opened fire, knocking the stranded trio to the ground, Draco ordered the shuttle to lift off. Defender One escaped the planet as the Star Destroyer Dauntless held a corridor of space open for them, taking the brunt of the War Hammer's attack and being destroyed in the process.[15]

"The news, bluntly put, is disastrous. My contact on Coruscant has just informed me that the Princess Marasiah had been taken to Korriban.""We could not rescue her from there if we had a thousand ships!"

Back on Bastion, Sinde was one of several Imperial Knights that responded to an alarm that a Sith ship had penetrated the Imperial world's net of droid mines. The ship had transmitted the proper authorization codes, and Sinde wondered if the codes had been attained by the Sith from a captured Imperial Knight. The ship had been commandeered on Agamar by Masters Rae and Rasi Tuum to effect their escape, although they were unable to rescue the Princess. Instead, they brought word that she was being taken to Coruscant. Later, at a meeting with the Emperor, Sinde learned that the Princess had been transferred from the capital to Korriban, the Sith's main stronghold. Sinde held the opinion that they could not rescue her from the planet with a thousand ships, but the Emperor knew something had to be done, giving Master Draco three hours to formulate a plan to either rescue her or kill before she broke under interrogation.[16] Draco, accompanied by Ganner Krieg and the Twi'lek Jedi Knight Shado Vao, successfully infiltrated Korriban and rescued the Princess, but Draco was captured by the Sith.[17] Following the rescue of the Princess, Sinde attended a memorial service on Bastion to honor Draco—who was believed to be dead—and the Knights who had fallen in battle on Agamar.[18]

It was soon learned that Darth Krayt was not dead. Despite being absent for months, the Sith Lord returned to take command of the Sith Empire, having healed himself through the Force following the injuries he sustained on Had Abbadon.[18]Darth Havok, a former Imperial Knight who had joined the Sith, tortured the captive Antares Draco on Korriban. From him, he learned that the Jedi had established a Hidden Temple on the planet Taivas. Havok relayed the information to Darth Krayt,[19] who tasked Grand AdmiralMorlish Veed to assault the Temple. Draco was subsequently frozen in carbonite, then released into the custody of the rogue Jedi, Cade Skywalker. Draco was thawed, and he confessed to breaking under torture and revealing the location of the Hidden Temple. The Jedi Council contacted their allies, the Galactic Alliance and the Fel Empire, and a plan to oppose the Sith Empire at Taivas was drawn up. While the Jedi engaged the Sith ground forces, Admiral Stazi and Emperor Fel would commit fleets to assist. Master Sinde commanded the Imperial forces, which rendezvous with their Alliance counterparts. As the Sith launched their ground assault, the Jedi sent a signal to Admiral Stazi, who ordered the fleets to jump to Taivas. As they exited hyperspace, Sinde gave the order for the Imperial ships to open fire.[20]

The allied ships inflicted heavy damage on the Sith-Imperial fleet, destroying the Ardent-class fast frigateIntruder in the opening salvo. Admiral Stazi encouraged Master Sinde to press the attack, proclaiming that the allied forces had the Sith trapped; Sinde, however, advised caution, reminding the admiral that victory had not yet been won. With the allied forces committed, Darth Krayt sprung his own trap. He had expected the Alliance and the Empire to commit forces to defend Taivas after releasing Master Draco into Skywalker's care, and had his own newly created Sith Troopers standing by to ambush the combined Alliance and Imperial forces. At Krayt's signal, a fleet of Dragon ships and Annihilator-class starfighters emerged from hyperspace and assaulted the allied ships. The Alliance battlecruiserStarrunner was destroyed by the opening barrage after the Sith vessels penetrated the ship's shields. Sinde immediately recalled all starfighters to protect his Star Destroyers, and wanted to know exactly what they were facing.[21]

The newly arrived Sith force did not differentiate between friend or foe, and attacked any ships or ground forces in their way. As the battle raged, the Jedi launched several of the ships that had been used to construct the Hidden Temple, hoping to evacuate the majority of the Order. One ship, carrying younglings, was targeted by the Sith Darth Rauder, who ordered Captain Gunn Yage of Skull Squadron to destroy the vessel. Yage, feeling that the Sith had no honor by ordering the deaths of children, used her starfighter's weapons to destroy Rauder's ship. Yage contacted her father, Moff Yage, on the Star Destroyer War Hammer orbiting Taivas, and informed him of her intention to defect to Roan Fel's forces. A Sith on the bridge of the Star Destroyer ordered the Sith-Imperial forces to kill Captain Yage; Moff Yage promptly executed the Sith, and joined her in defecting, encouraging other ships and captains to join him. Master Sinde accepted Yage's offer of defection, welcoming him back into the Imperial fleet on behalf of the Emperor. The Sith forces continued to assault the allied fleet and the Hidden Temple, until Jedi Masters T'ra Saa and "Bantha" Rawk released a large amount of Force energy in their dying moments. The energy wave swept aside the enemy ships, allowing the evacuation vessels to escape Taivas. Seeing a chance to escape, Admiral Stazi ordered all allied ships to escape along emergency hyperspace vectors, retreating to Bastion.[21]

"Sia, Treis, Draco -- you will remain here with me on the flagship. I need those nearby whose loyalty to me is a certainty."

―Emperor Roan Fel, aboard the Jagged Fel, just prior to the Battle of Coruscant[src]

On Bastion, three days after the battle at Taivas, Sinde—along with Emperor Fel, Hogrum Chalk, Admiral Stazi, and Jedi Master Tili Qua—watched a medical examination of one of Darth Krayt's Sith troopers who had been captured by the crew of Cade Skywalker's ship, the Mynock, during the fighting. Before the trooper died, he revealed that there were millions of others like him and that they were devoted to Krayt. With Hogrum Chalk's urging, Emperor Fel convinced Stazi and the Jedi Council to attack Coruscant immediately as the Sith would not be expecting a retaliatory attack so soon after Taivas. A strike team comprised of Imperial Knights and Jedi, led by Cade Skywalker aboard the Mynock, would infiltrate Coruscant ahead of the main battle fleet to deactivate the orbital defenses. Sinde was stationed on the Imperial flagship, the Jagged Fel, at Emperor Fel's request, as he wanted his most trusted and loyal Knights at his side. The strike team successfully infiltrated Coruscant, using information supplied by Nyna Calixte. Calixte's role in warning Fel of the assault on Agamar had been discovered, and her execution had been ordered. Calixte survived an assassination attempt perpetrated by Morlish Veed, and subsequently hooked up with the allied forces of the Empire and the Alliance. The strike team completed their mission, neutralizing the orbital defenses and allowing the allied fleet to engage Coruscant's ground-based defenses and the Annihilator-class starfighters of Krayt's Sith troopers.[22]

Despite the strike team's success, the Sith forces proved to be too strong for the allied fleet. Emperor Fel, believing the battle to be lost, intended to release a virulent toxin capable of wiping out all life on a planet, regardless of species, that had been designed by one of Krayt's Sith, Darth Maladi. Maladi had previously been captured by Imperial forces, and had struck a deal with Fel to create the toxin in exchange for safe haven and the life of Cade Skywalker. In reality, Maladi's capture had been arranged by Krayt to give Fel the toxin, which Krayt and his Sith were immune to by design. Fel intended to use the toxin on Coruscant to eliminate Krayt and his followers once and for all, feeling that the loss of a single planet was worth the sacrifice for killing the Sith Lord. As he prepared to release it, Sinde, alongside Fel's daughter and Antares Draco, implored his old friend to step away from the launch mechanism. Fel responded by Force-pushing his daughter and Sinde into the bulkhead behind them. Draco, finally realizing that his duty was to the Force as embodied by the Emperor rather than the Emperor himself, dueled and killed Fel, fulfilling his oath to prevent his liege from falling to the Dark Side. On Coruscant, Skywalker killed Darth Krayt, causing his Sith troopers to go mad and forcing Darth Nihl to order the retreat of all Sith Imperial forces from the planet. With victory achieved, the allied forces established the Galactic Federation Triumvirate to rule the galaxy, consisting of the new Empress, Marasiah Fel, Jedi Master K'kruhk, and Admiral Gar Stazi.[23]

By 138 ABY, Treis Sinde was the eldest Imperial Knight in service to Emperor Fel. His skin was tanned, and his hair and beard were pure white.[1] Pledged to serve the Emperor and the Empire-in-exile like all Imperial Knights,[4] Sinde was a level-headed and pragmatic man, able to see the larger picture of galactic affairs.[1] However, Sinde held to the belief that while Imperial Knights owed their allegiance to the Emperor, they were meant to follow the Force as embodied by the Emperor, not to obey him over its will. Sinde was willing to disobey direct orders to follow the will of the Force, and was dismayed that many of the younger knights, including his own former apprentice Sigel Dare, held loyalty to the Emperor as more important than the needs of the Force.[3]

When sabotaging the Imperious, Sinde planned for the explosives to go off away from Dac, so that the native Mon Calamari would hopefully not be blamed for their act. He did not share Sigel Dare's views that all non-Imperial's were technically their enemies, and often counseled the younger Knight that she needed to look at the bigger picture. While Dare did not always agree with him, she respected Sinde's wisdom and decisions.[1] He was also fully aware that the Mon Calamari Rangers could not defeat the Empire and the Sith, and instead counseled them to focus on surviving long enough for outside assistance to arrive.[7]

Sinde also had no compunctions about sacrificing others to achieve the greater good, as shown when he informed Captain Tanquar of the Rangers that they should forget about protecting Mon Calamari refugees from the Leviathan, as it was clearly a Sith scheme to draw the Rangers out of hiding.[2] However, the Knight was also willing to sacrifice himself if it would help the completion of his mission, such as engaging Darth Azard in combat rather than seek to escape Dac himself since he knew that informing Stazi of the explosives on board the Imperious was important as he saw the wisdom in a possible alliance between the Galactic Alliance and Fel's Empire-in-exile.[1]

Sinde was unafraid of speaking his mind, even if what he said threatened to make him unpopular to those he was speaking to.[7] Emperor Fel II regarded Sinde to be stubborn, and informed his son, Roan Fel, of this fact. However, despite this, he was deferential towards his Master, Emperor Fel, even when he felt that his Liege's orders went against what Sinde thought to be morally right.[2]

A capable warrior, Sinde could fight as effectively underwater as he could on the ground. Sinde also had a talent for command, as he had previously commanded an Imperial mission to the Unknown Regions,[7] and was given the responsibility of leading the team of himself and Master Dare to Dac,[1] as well as commanding the fleet sent to support the Jedi Order at Taivas.[21] He was also a shrewd strategist and tactician, able to devise plans to achieve objectives such as planting multiple explosive charges on the Imperious,[1] capturing an Acklay battle fortress,[7], as well as devising an ad hoc strategy to defeat the Leviathan shortly after learning of its existence.[2] He was also an effective teacher in the ways of the Force,[2] have trained Sigel Dare to knighthood,[3] and was required by Emperor Fel to train new Imperial Knights even though Fel had other Knights available, and Sinde was assisting the Mon Calamari resistance at the time.[2]

Sinde and Roan Fel were close friends and confidants, which stemmed from their days as apprentices together. When Fel began to fear that he was being tempted with corruption by the last seven years of war against the Sith and his desire to possess the Muur Talisman, he recalled Sinde to his side so that he could benefit from the experienced Knight's wisdom and counsel.[5] Sinde's loyalty to the Emperor was absolute, and in return, Fel trusted the Knight implicitly.[22] However, Sinde had sworn an oath to serve the Force as embodied by the Emperor, and to prevent the Emperor from falling to the Dark Side. When Fel intended to kill billions of innocents on Coruscant—including his allies—by releasing the Omega Red toxin in an effort to kill Krayt and his Sith, Sinde stood against him and implored him to reconsider. Fel attacked Sinde, and was only stopped from releasing the toxin when Antares Draco dueled and killed him.[23]

Sinde was a fully trained Imperial Knight, and was skilled in employing the Force to repel attackers. He was also skilled with the use of a lightsaber—wielding one of the same design as every other Knight—and could use it to both effectively deflect incoming blaster bolts and duel a Sith Lord.[1] His lightsaber was also capable of functioning underwater.[7] Sinde could project a protection bubble to safeguard himself from harm, as he did when caught in a fuel tank explosion on the Sea Lion,[7] and could use the power of animal friendship to take command of a large number of Devilsquids and direct them to attack the Leviathan.[2]